Various types of batteries have been developed heretofore, and in every battery, a packaging material is an essential member for sealing battery elements such as an electrode and an electrolyte. Metallic packaging materials have been often used heretofore as battery packagings.
On the other hand, batteries are required to be diversified in shape and to be thinned and lightened with improvement of performance of electric cars, hybrid electric cars, personal computers, cameras, mobile phones and so on. However, metallic battery packaging materials that have often been heretofore used have the disadvantage that it is difficult to keep up with diversification in shape, and there is a limit on weight reduction.
Thus, a film-shaped laminated body including a base material layer, an adhesive layer, a barrier layer and a sealant layer in this order has been proposed as a battery packaging material which is easily processed into diverse shapes and which can be thinned and lightened (see, for example, Patent Document 1). The film-shaped battery packaging material is formed in such a manner that a battery element can be sealed by heat-welding the peripheral edge by heat sealing with the sealant layers facing each other.
On the other hand, in recent years, demand for downsizing and thinning of batteries has been increasingly grown, and in conformity to the demand, further thinning of film-shaped battery packaging materials has been required. Examples of the method for thinning the whole of a film-shaped battery packaging material include a method in which a base material layer including a resin film having a thickness of about 10 to 20 μm is thinned. However, thinning of the resin film has limitations in terms of production, and also has the problem that the processing cost required for thinning of the resin film causes an increase in production cost of a battery packaging material.
A coating layer formed by applying a thermosetting resin can be considerably reduced in thickness as compared to the resin film, and therefore replacement of an adhesive layer and a base material layer, which are laminated on a barrier layer, by a coating layer formed of a thermosetting resin is effective for thinning the whole of a film-shaped battery packaging material. When a coating layer is provided in place of an adhesive layer and a base material layer as described above, the coating layer is required to have a thickness which ensures that insulation quality can be imparted for securing the basic performance of the coating layer. Examples of the method for providing a coating layer, which can impart insulation quality, on a barrier layer using a conventional technique include a method in which a barrier layer is thickly coated with a thermosetting resin, and a method in which a barrier layer is thinly coated with a thermosetting resin repeatedly over a plurality of times to laminate a plurality of coating layers on the barrier layer. However, the former method has the disadvantage that bubbles are easily generated in the coating layer due to the thick coating, so that it is difficult to form a coating layer free from pinholes. Both the former and latter methods have the problem that when a coating layer is formed using a thermosetting resin using a conventional technique, it is required to perform aging under a high-temperature condition for several days to several weeks as a curing step, and therefore the lead time is increased, so that product defects occur due to exposure to a high-temperature condition and a temperature change for a long period of time. Particularly, the latter method is not practical because for forming a plurality of coating layers, it is necessary to carry out a curing step over a plurality of times, so that a very long lead time is needed.
Further, when a coating layer is provided as an outermost layer in place of an adhesive layer and a base material layer in a film-shaped battery packaging material, it is also important that the coating layer has resistance to deposition of chemicals such as an electrolytic solution, an acid, an alkali and an organic solvent (chemical resistance) as basic performance in addition to insulation quality. It is also important that the film-shaped battery packaging material has excellent moldability and its surface has slippage for improving moldability/processability in press molding and embossing, and operability.
In view of these conventional techniques, it is earnestly desired to develop a battery packaging material which is made thin by providing a coating layer as an outermost layer on a barrier layer, the battery packaging material being capable of reducing the lead time, and capable of being given functionalities such as moldability, chemical resistance and slippage.
In recent years, there has been no shortage of demand for further improvement of battery performance, and accordingly, it has been required to increase the battery capacity. A film-shaped battery packaging material is processed into a predetermined shape by deep drawing molding etc. to seal a battery element, and therefore for increasing the battery package, the moldability of the film-shaped battery packaging material should be improved to increase the molding depth (extension during molding).
In view of these conventional techniques, a technique has been developed for achieving excellent moldability and reducing the lead time in a battery packaging material which is made thin by providing a coating layer in place of an adhesive layer and a base material layer.